upgrade to libp2p 0.52 (#4431)

## Issue Addressed

Upgrade libp2p to v0.52

## Proposed Changes
- **Workflows**: remove installation of `protoc`
- **Book**: remove installation of `protoc`
- **`Dockerfile`s and `cross`**: remove custom base `Dockerfile` for cross since it's no longer needed. Remove `protoc` from remaining `Dockerfiles`s
- **Upgrade `discv5` to `v0.3.1`:** we have some cool stuff in there: no longer needs `protoc` and faster ip updates on cold start
- **Upgrade `prometheus` to `0.21.0`**, now it no longer needs encoding checks
- **things that look like refactors:** bunch of api types were renamed and need to be accessed in a different (clearer) way
- **Lighthouse network**
	- connection limits is now a behaviour
	- banned peers no longer exist on the swarm level, but at the behaviour level
	- `connection_event_buffer_size` now is handled per connection with a buffer size of 4
	- `mplex` is deprecated and was removed
	- rpc handler now logs the peer to which it belongs

## Additional Info

Tried to keep as much behaviour unchanged as possible. However, there is a great deal of improvements we can do _after_ this upgrade:
- Smart connection limits: Connection limits have been checked only based on numbers, we can now use information about the incoming peer to decide if we want it
- More powerful peer management: Dial attempts from other behaviours can be rejected early
- Incoming connections can be rejected early
- Banning can be returned exclusively to the peer management: We should not get connections to banned peers anymore making use of this
- TCP Nat updates: We might be able to take advantage of confirmed external addresses to check out tcp ports/ips


Co-authored-by: Age Manning <Age@AgeManning.com>
Co-authored-by: Akihito Nakano <sora.akatsuki@gmail.com>

beacon_node/lighthouse_network/src/rpc/protocol.rs

@@ -7,7 +7,7 @@ use crate::rpc::{
 use futures::future::BoxFuture;
 use futures::prelude::{AsyncRead, AsyncWrite};
 use futures::{FutureExt, StreamExt};
-use libp2p::core::{InboundUpgrade, ProtocolName, UpgradeInfo};
+use libp2p::core::{InboundUpgrade, UpgradeInfo};
 use ssz::Encode;
 use ssz_types::VariableList;
 use std::io;
@@ -313,6 +313,12 @@ pub struct ProtocolId {
     protocol_id: String,
 }
 
+impl AsRef<str> for ProtocolId {
+    fn as_ref(&self) -> &str {
+        self.protocol_id.as_ref()
+    }
+}
+
 impl ProtocolId {
     /// Returns min and max size for messages of given protocol id requests.
     pub fn rpc_request_limits(&self) -> RpcLimits {
@@ -407,12 +413,6 @@ impl ProtocolId {
     }
 }
 
-impl ProtocolName for ProtocolId {
-    fn protocol_name(&self) -> &[u8] {
-        self.protocol_id.as_bytes()
-    }
-}
-
 /* Inbound upgrade */
 
 // The inbound protocol reads the request, decodes it and returns the stream to the protocol